A chromatography instrument acquires data expressing a chromatogram with time on the X axis and signal strength (output voltage or the like) on the Y axis (hereinafter referred to as chromatogram data) by analyzing a sample. Chromatographic data processing devices detect peaks occurring in a chromatogram of this kind, and identify the substance corresponding to a peak from the location of the peak (retention time) by referring to a pre-set identification table, as well as calculating the concentration and quantity of that substance from the height and area of the peak.
In data processing devices of this kind, there is generally a limit to the size of signals that can be processed, arising from the constraints of the hardware of the signal processing circuit such as the A/D converter, meaning that computations cannot be performed accurately if signals of a size exceeding the upper or lower limit are input.
Furthermore, entirely unrelated to this signal processing limit, the reliability of detection results will differ depending on the level of the signal from the chromatography instrument's detector. For example, in the case of a UV-visible spectrophotometer, photodiode array detector, or the like, which are used as detectors in liquid chromatographs, nonlinearity typically becomes more pronounced as the concentration of components in the sample increases, as shown in FIG. 10, which impairs assay accuracy. Accordingly, it is desirable to perform analysis in such a way that the concentration of the target component in the sample is within a designated range (dynamic range).